CN111684717A

CN111684717A - Bonded body of piezoelectric material substrate and support substrate

Info

Publication number: CN111684717A
Application number: CN201880088584.9A
Authority: CN
Inventors: 多井知义; 服部良祐
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2018-02-13
Filing date: 2018-12-27
Publication date: 2020-09-18
Anticipated expiration: 2038-12-27
Also published as: JP7210497B2; DE112018006860T5; TWI791080B; JP6801109B2; KR102282238B1; JP2020102856A; KR20200096987A; JPWO2019159555A1; DE112018006860B4; US10998878B2; CN111684717B; TW201935615A; US20200373905A1; WO2019159555A1

Abstract

The present invention provides a bonded body of a support substrate and a piezoelectric material substrate made of a material selected from the group consisting of lithium niobate and the like, wherein the bonding strength of the bonded body is improved. The joined bodies 7 and 7A include: a support substrate 4; piezoelectric material substrates 1, 1A made of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; and an amorphous layer 5 which exists between the support substrate 4 and the piezoelectric material substrates 1 and 1A. The amorphous layer 5 contains one or more metal atoms selected from the group consisting of niobium and tantalum, atoms constituting the support substrate, and oxygen atoms. The concentration of the metal atoms in the amorphous layer 5 is higher than that of the oxygen atoms and is 20-65 atomic%.

Description

Bonded body of piezoelectric material substrate and support substrate

Technical Field

The present invention relates to a bonded body of a piezoelectric material substrate and a support substrate.

Background

For the purpose of realizing a high-performance semiconductor element, a semiconductor element containing high-resistance Si/SiO is widely used₂Thin film/Si thin film SOI substrate. In realizing the SOI substrate, plasma activation is used. This is because the bonding can be performed at a relatively low temperature (400 ℃). Similar inclusion of Si/SiO has been proposed to improve the characteristics of piezoelectric devices₂A thin film/piezoelectric thin film composite substrate (patent document 1). In patent document 1, a piezoelectric material substrate containing lithium niobate or lithium tantalate and a silicon substrate provided with a silicon oxide layer are activated by an ion implantation method and then bonded.

A multilayer filter in which one or more dielectric films are formed at a bonding interface has also been proposed (patent document 2).

Patent document 3 describes that lithium tantalate is bonded to sapphire or ceramic by a plasma activation method through a silicon oxide layer.

Non-patent document 1 describes that O is continuously irradiated₂RIE (13.56MHz) plasma and N₂Thereby bonding the lithium tantalate substrate and the silicon substrate provided with the silicon oxide layer to each other by microwave (2.45GHz) plasma.

In the presence of Si and SiO₂In the plasma activated bonding of/Si, Si-O-Si bonds are formed at the bonding interface, thereby obtaining sufficient bonding strength. In addition, Si is oxidized to SiO at the same time₂This improves the smoothness, and promotes the bonding on the outermost surface (non-patent document 2).

In patent document 4, an amorphous layer containing tantalum, silicon, argon, and oxygen is generated along the interface between a silicon substrate and a lithium tantalate substrate by activating the surface of the silicon substrate and the surface of the lithium tantalate substrate with an argon beam and then bonding the surfaces.

Documents of the prior art

Non-patent document

Non-patent document 1: ECS Transactions,3(6)91-98(2006)

Non-patent document 2: j.applied Physics 113,094905(2013)

Patent document

Patent document 1: japanese laid-open patent publication 2016 & 225537

Patent document 2: japanese patent No. 5910763

Patent document 3: japanese patent No. 3774782

Patent document 4: WO 2017-134980A 1

Disclosure of Invention

However, it was found that if direct bonding of a silicon substrate and a lithium tantalate substrate by surface activation is attempted as described in patent document 4, the bonding strength is low, and peeling occurs when stress is applied to the bonded body by polishing or the like. The reason why the bonding strength is increased is considered to be that tantalum atoms are diffused greatly in the amorphous layer, but it is not clear that the bonding strength is not improved to a certain extent or more.

The present invention addresses the problem of improving the bonding strength of a bonded body of a support substrate and a piezoelectric material substrate made of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate.

The present invention relates to a bonded body comprising:

supporting a substrate;

a piezoelectric material substrate formed of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; and

an amorphous layer containing one or more metal atoms selected from the group consisting of niobium and tantalum, atoms constituting the support substrate, and oxygen atoms, and being present between the support substrate and the piezoelectric material substrate,

the joint body is characterized in that,

the concentration of the metal atoms in the amorphous layer is higher than that of the oxygen atoms and is 20-65 atomic%.

Effects of the invention

The inventors of the present invention have studied the cause of the decrease in bonding strength of a bonded body when a support substrate and a piezoelectric material substrate made of lithium niobate or the like are directly bonded, and the peeling easily occurs when the piezoelectric material substrate is processed.

That is, as described in patent document 4, it was found that if an attempt is made to directly bond a silicon substrate and a lithium tantalate substrate by surface activation, the bonding strength is low, and peeling occurs when stress is applied to the bonded body by polishing or the like. In this junction structure, since tantalum atoms are diffused greatly in the amorphous layer, the junction strength should be increased.

Therefore, various attempts have been made to change the conditions and energy for activating the surface of the support substrate and the surface of the piezoelectric material substrate, and various studies have been made on the state and bonding strength of the amorphous layer. As a result, it was found that not only one or more metal atoms selected from the group consisting of tantalum and niobium were diffused in the amorphous layer, but also the concentration of the metal atoms was made higher than that of oxygen atoms, so that the bonding strength was significantly improved.

Drawings

In fig. 1, (a) shows a piezoelectric material substrate 1, and (b) shows a state in which a bonding surface 1a of the piezoelectric material substrate 1 is activated to generate an activated bonding surface 1 c.

In fig. 2, (a) shows the support substrate 4, and (b) shows a state in which the bonding surface 4a of the support substrate 4 is activated to generate an activated bonding surface 4 c.

In fig. 3, (a) shows a bonded body 7 obtained by directly bonding the piezoelectric material substrate 1 and the support substrate 4, (b) shows a state in which the piezoelectric material substrate 1A of the bonded body 7 is polished to be thin, and (c) shows the acoustic wave device 10.

Detailed Description

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings as appropriate.

First, as shown in fig. 1(a), a piezoelectric material substrate 1 having a pair of

surfaces

1a and 1b is prepared. In this example, 1a is a bonding surface. Next, as shown in fig. 1(b), an Ar beam is irradiated to the bonding surface 1a of the piezoelectric material substrate 1 as indicated by an arrow a, thereby obtaining a surface-activated bonding surface 1 c.

On the other hand, as shown in fig. 2(a), a support substrate 4 having a pair of

surfaces

4a, 4b is prepared. In this example, 4a is a bonding surface. Next, as shown in fig. 2(B), the surface 4a of the support substrate 4 is irradiated with an Ar beam to activate the surface, as indicated by arrow B, thereby forming an activated bonding surface 4 c.

Next, as shown in fig. 3(a), the activated bonding surface 1c on the piezoelectric material substrate 1 and the activated bonding surface 4c on the support substrate 4 are brought into contact with each other and directly bonded to each other, thereby obtaining a bonded body 7. The amorphous layer 5 is formed on the junction structure 7. In this state, an electrode may be provided on the piezoelectric material substrate 1. However, as shown in fig. 3(b), it is preferable that the main surface 1b of the piezoelectric material substrate 1 is processed to thin the substrate 1, thereby obtaining a thinned piezoelectric material substrate 1A. And 1d is a processed surface. Next, as shown in fig. 3(c), a predetermined electrode 8 is formed on the processed surface 1d of the piezoelectric material substrate 1A of the joined body 7A, and the acoustic wave device 10 can be obtained.

Hereinafter, each constituent element of the present invention will be described in order.

(amorphous layer)

In the present invention, the amorphous layer 5 present between the support substrate 4 and the piezoelectric material substrate 1 contains one or more metal atoms selected from the group consisting of niobium and tantalum, atoms constituting the support substrate, and oxygen atoms, and the concentration of the metal atoms in the amorphous layer is 20 to 65 atomic% higher than the concentration of oxygen atoms. By providing the amorphous layer 5, the bonding strength between the support substrate 4 and the piezoelectric material substrate 1 can be improved.

The one or more metal atoms selected from the group consisting of niobium and tantalum may be niobium alone, tantalum alone, or both niobium and tantalum. In the case where the amorphous layer 5 contains both niobium and tantalum, the concentration of the metal atoms is the sum of the niobium concentration and the tantalum concentration. In addition, when the atoms constituting the support substrate 4 are of a single type, the atoms constituting the amorphous layer 5 are also of a single type. In the case where there are a plurality of kinds of atoms constituting the support substrate 4, the atoms constituting the support substrate 4 are one or more kinds of these atoms. However, niobium, tantalum, and oxygen are excluded from atoms constituting the support substrate 4.

According to the present invention, the concentration of the metal atoms in the amorphous layer 5 is higher than the concentration of oxygen atoms and is 20 to 65 atomic%. From the viewpoint of the present invention, the concentration of the metal atoms in the amorphous layer 5 is more preferably 20.3 atomic% or more, and still more preferably 63.2 atomic% or less.

In a preferred embodiment, when the concentration of the metal atoms in the amorphous layer is 1.0, the concentration of oxygen atoms is 0.30 to 0.65, and the concentration of oxygen atoms is more preferably 0.32 to 0.62, whereby the bonding strength is further improved.

The concentration of oxygen atoms in the amorphous layer 5 is preferably 12 to 26 atomic%.

In the amorphous layer 5, atoms constituting the support substrate 4 are atoms other than tantalum, niobium, and oxygen atoms. The atom is preferably silicon. From the viewpoint of the present invention, the concentration of the atoms constituting the supporting substrate 4 in the amorphous layer 5 is preferably 13 to 64 atomic%.

In addition, the amorphous layer 5 may contain argon or nitrogen. The concentration of argon and nitrogen is preferably 1.0 to 5.0 atomic%.

The thickness of the amorphous layer 5 is preferably 4 to 12 nm.

In addition, the presence of the amorphous layer 5 was confirmed as follows.

A measuring device:

microstructure observation was performed using a transmission electron microscope (Hitachi high tech H-9500).

The measurement conditions were as follows:

the sample thinned by the FIB (focused ion beam) method was observed at an acceleration voltage of 200 kV.

The concentration of each atom in the amorphous layer 5 was measured as follows.

A measuring device:

elemental analysis was carried out using an elemental analysis apparatus (Japanese Electron JEM-ARM 200F).

The measurement conditions were as follows:

(supporting substrate)

The material of the support substrate 4 is not particularly limited, and the following materials can be exemplified.

The material of the support substrate 4 preferably includes a material selected from the group consisting of silicon, crystal, sialon, mullite, sapphire, and translucent alumina. This can further improve the temperature characteristics of the frequency of the acoustic wave device.

(piezoelectric Material substrate)

As the piezoelectric material substrate 1 used in the present invention, Lithium Tantalate (LT) single crystal, Lithium Niobate (LN) single crystal, or lithium niobate-lithium tantalate solid solution is used. These materials have a high propagation speed of elastic waves and a large electromechanical coupling coefficient, and therefore, are suitable as elastic surface wave devices for high frequency and wide frequency bands.

The normal direction of the main surface of the piezoelectric material substrate 1 is not particularly limited, and when the piezoelectric material substrate 1 is formed of LT, for example, a piezoelectric material substrate rotated by 32 to 50 ° from the Y axis to the Z axis about the X axis which is the propagation direction of the elastic surface wave and expressed by euler angles (180 °, 58 to 40 °, and 180 °) is preferably used because the propagation loss is small. When the piezoelectric material substrate is formed of LN, (a) a piezoelectric material substrate which is rotated by 37.8 ° from the Z axis to the-Y axis about the X axis which is the propagation direction of the elastic surface wave and expressed by euler angles of (0 °, 37.8 °,0 °) is used, and therefore, the electromechanical coupling coefficient is preferably large; alternatively, (b) a piezoelectric material substrate is preferably used which is rotated by 40 to 65 ° from the Y axis to the Z axis about the X axis which is the propagation direction of the elastic surface wave, and which has euler angles of (180 °, 50 to 25 °, 180 °), since high sound velocity can be obtained. The size of the piezoelectric material substrate is not particularly limited, and for example, the substrate has a diameter of 100 to 200mm and a thickness of 0.15 to 50 μm.

(surface activation treatment)

The surface 1a of the piezoelectric material substrate 1 and the surface 4a of the support substrate 4 are subjected to activation treatment. At this time, the surface 1a of the piezoelectric material substrate 1 and the surface 4a of the support substrate 4 can be activated by irradiating the surface 1a of the piezoelectric material substrate 1 and the surface 4a of the support substrate 4 with a neutral beam. At this time, the atomic concentration of the joining interface can be controlled by controlling the voltage, current, beam atomic gas flow rate, and beam irradiation time for irradiating the neutral beam.

In the case of surface activation by a neutral beam, it is preferable to generate a neutral beam and irradiate the neutral beam using an apparatus such as that described in japanese patent application laid-open No. 2014-086400. That is, as the beam source, a saddle-field type high-speed atomic beam source is used. Then, an inert gas is introduced into the chamber, and a high voltage is applied from a dc power supply to the electrodes. Thus, electrons e are moved by a saddle-field-type electric field generated between the electrode (positive electrode) and the case (negative electrode), and an atomic beam and an ion beam generated from an inert gas are generated. The ion beam in the beam reaching the grid is neutralized at the grid, so that a neutral atom beam is emitted from the high-speed atom beam source. The atomic species constituting the beam are preferably inert gases (argon, nitrogen, etc.).

The voltage for activation by beam irradiation is preferably 0.2 to 2.0kV, the current is preferably 20 to 200mA, the flow rate of the inert gas is preferably 20 to 80sccm, and the beam irradiation time is preferably 15 to 300 sec.

Next, the activated surfaces are brought into contact with each other in a vacuum atmosphere to perform bonding. The temperature at this time is room temperature, and specifically, is preferably 40 ℃ or lower, and more preferably 30 ℃ or lower. The temperature at the time of bonding is particularly preferably 20 ℃ to 25 ℃. The pressure during bonding is preferably 100 to 20000N.

Next, the activated bonding surface 1c of the piezoelectric material substrate 1 and the activated bonding surface 4c of the support substrate 4 are brought into contact with each other to be bonded. Then, annealing treatment is preferably performed to improve the bonding strength. The temperature during the annealing treatment is preferably 100 ℃ to 300 ℃.

(elastic wave element)

The bonded bodies 7 and 7A of the present invention can be particularly preferably used for the elastic wave device 10.

As the acoustic wave element 10, an elastic surface wave device, a lamb wave element, a thin film resonator (FBAR), and the like are known. For example, a surface acoustic wave device is obtained by providing an IDT (inter digital transducer) electrode (also referred to as a comb-shaped electrode or an interdigital electrode) on the input side for exciting a surface acoustic wave and an IDT electrode on the output side for receiving a surface acoustic wave on the surface of a piezoelectric material substrate. When a high-frequency signal is applied to the IDT electrode on the input side, an electric field is generated between the electrodes, and a surface acoustic wave is excited and propagated on the piezoelectric material substrate. The propagating surface acoustic wave can be acquired as an electric signal from the IDT electrode on the output side provided in the propagation direction.

The material constituting the electrode 8 on the piezoelectric material substrate 1A is preferably aluminum, an aluminum alloy, copper, or gold, and more preferably aluminum or an aluminum alloy. As the aluminum alloy, an aluminum alloy in which 0.3 to 5 wt% of Cu is mixed in Al is preferably used. In this case, Ti, Mg, Ni, Mo, Ta may be used instead of Cu.

Examples

The joined body 7A is produced by the method described with reference to fig. 1 to 3.

Specifically, a lithium tantalate substrate (LT substrate) having an oriented flat surface portion (OF portion), a diameter OF 4 inches, and a thickness OF 250 μm was used as the piezoelectric material substrate 1. Further, as the support substrate 4, a silicon substrate having an OF portion, a diameter OF 4 inches, and a thickness OF 230 μm was prepared. The LT substrate used was a 46 ° Y cut X-propagation LT substrate in which the propagation direction of a Surface Acoustic Wave (SAW) was X and the cut-out angle was a rotational Y-cut plate. The surface 1a of the piezoelectric material substrate 1 and the surface 4a of the support substrate 4 were mirror-polished so that the arithmetic average roughness Ra was 1 nm. The arithmetic mean roughness was evaluated by an Atomic Force Microscope (AFM) in a field of view of a square of 10 μm in the vertical direction × 10 μm in the horizontal direction.

Next, the surface 1a of the piezoelectric material substrate 1 and the surface 4a of the support substrate 4 are cleaned to remove stains, and then introduced into a vacuum chamber. Vacuum pumping is carried out to 10^－6Pa is not less than 10^－5After Pa, 135KJ of high-speed atomic beam was irradiated to the bonding surfaces 1a and 4a of the substrates. Next, the beam irradiation surface of the piezoelectric material substrate 1 (after activation) is irradiated with a beamBonding surface of (1) 1c and the activated bonding surface 4c of the support substrate 4, followed by pressing at 10000N for 2 minutes to bond the two substrates.

Here, as shown in tables 1 and 2, the beam irradiation energy (FAB irradiation amount) was changed. The presence of the amorphous layer 5 along the bonding interface of each of the bonded bodies 7 obtained was confirmed, and the concentration of each atom in the amorphous layer 5 was measured, and the results are shown in tables 1 and 2. The relative ratios of the concentrations of the tantalum atoms in the amorphous layer 5 are also shown in tables 1 and 2, assuming that the concentration of the tantalum atoms is 1.00.

The joint strength of the joined body 7 of each example was evaluated by the crack propagation method and is shown in tables 1 and 2.

[ Table 1]

[ Table 2]

In comparative examples 1 and 2, the concentration of tantalum in the amorphous layer 5 was low (16.6 atomic% in comparative example 1 and 9.2 atomic% in comparative example 2), and the diffusion of tantalum was insufficient, and therefore the bonding strength was reduced (0.8J/m in comparative example 1)²The bonding strength in comparative example 2 was 0.2J/m²)。

In comparative example 3, the tantalum concentration in the amorphous layer 5 was high (75.3 atomic% in comparative example 3), and the bonding strength was reduced (0.5J/m in comparative example 3)²)。

In comparative example 4, although the tantalum atoms in the amorphous layer 5 were moderately diffused (38.5 atomic% in comparative example 4), the concentration of the tantalum atoms was lower than the concentration of the oxygen atoms (when the concentration of the tantalum atoms was 1.0, the concentration of the oxygen atoms was 1.26 in comparative example 4), and as a result, the bonding strength was reduced (the bonding strength in comparative example 4 was 1.0J/m)²)。

On the other hand, in examples 1 to 3 of the present invention, high bonding strength was obtained. Specifically, theIn examples 1 to 3, the tantalum concentration in the amorphous layer 5 was moderately diffused (41.5 atomic% in example 1, 20.3 atomic% in example 2, and 63.2 atomic% in comparative example 3), and the tantalum atom concentration was higher than the oxygen atom concentration (when the tantalum atom concentration was 1.0, the oxygen atom concentration was 0.42 in example 1, 0.62 in example 2, and 0.32 in example 3). As a result, the bonding strength between the piezoelectric material substrate 1 and the support substrate 4 can be improved (2.2J/m in example 1)²In example 2, the concentration was 1.8J/m²Example 3 shows a value of 1.9J/m²)。

The same results were obtained when a lithium niobate substrate (LN substrate) was used instead of the lithium tantalate substrate (LT substrate) as the piezoelectric material substrate 1.

Specifically, as shown in example 4 of table 3, the niobium atoms in the amorphous layer 5 were moderately diffused (59.6 atomic% in example 4), and the concentration of the niobium atoms was higher than the concentration of the oxygen atoms (when the concentration of the niobium atoms was 1.0, the concentration of the oxygen atoms was 0.43 in example 4). As a result, the bonding strength between the piezoelectric material substrate 1 and the support substrate 4 can be improved (2.0J/m in example 4)²)。

[ Table 3]

Claims

1. A joined body, comprising:

supporting a substrate;

the joint body is characterized in that,

2. The junction body according to claim 1,

when the concentration of the metal atoms in the amorphous layer is set to be 1.0, the concentration of the oxygen atoms is 0.30-0.65.

3. The junction body according to claim 1 or 2,

the amorphous layer further includes argon atoms.

4. The junction body according to any one of claims 1 to 3,

the support substrate comprises silicon.

5. The junction body according to any one of claims 1 to 4,

the thickness of the piezoelectric material substrate is 50 [ mu ] m or less.